Redeemable Preferred Stock and Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 10, 2020	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Temporary Equity And Stockholders Equity [Line Items]
Common stock, shares authorized		180,000,000			180,000,000		180,000,000	40,000,000
Temporary equity preferred stock, shares authorized		1,000,000			1,000,000		1,000,000	1,000,000
Temporary equity preferred stock, par value		$ 0.001			$ 0.001		$ 0.001	$ 0.001
Temporary equity preferred stock, shares issued		0			0		0	70,000
Temporary equity preferred stock, shares outstanding		0			0		0	70,000
Compensation expense related to stock options		$ 0.8	$ 0.5		$ 1.6	$ 1.2
Total unrecognized compensation expense		$ 1.4			$ 1.4		$ 1.4
Unrecognized share based compensation expense to be recognized over weighted-average period		1 year 2 months 12 days
Warrant expiration period	5 years
Proceeds from Offering	$ 6.9
Combined purchase price of share and warrant	$ 0.64
Other offering expenses	$ 0.7
Expected term (years)		5 years 6 months	6 years 1 month 6 days		5 years 6 months	6 years 1 month 6 days
Volatility		103.10%	85.00%		102.80%	85.80%
Risk-free interest rate		0.36%	2.50%		0.37%	2.60%
Outstanding stock options, RSUs and warrants excluded from diluted loss per share		18,500,000		5,700,000	18,500,000	5,700,000
Common Stock And Warrants
Temporary Equity And Stockholders Equity [Line Items]
Exercise price of warrants		$ 0.42			$ 0.42		$ 0.42
Proceeds of common stock and warrants					$ 6.2
Expected term (years)					5 years
Closing price of common stock					$ 0.54
Volatility					109.80%
Risk-free interest rate					0.45%
Dividend yield					0.00%
Allocation to common stock and warrants before issuance costs					$ 3.9
Allocation to common stock and warrants before issuance costs					$ 3.0
Restricted Stock Units (RSUs)
Temporary Equity And Stockholders Equity [Line Items]
Granted					1.6
Cancelled RSU due to non achievement of performance targets					1.0
2002 Stock Incentive Plan
Temporary Equity And Stockholders Equity [Line Items]
Common stock authorized for issuance		3,100,000			3,100,000		3,100,000
Common stock issued pursuant to options exercised					1,000,000
Options and restricted stock units outstanding		1,100,000			1,100,000		1,100,000
Options available for future grants		0			0		0
2018 Long-Term Incentive Plan
Temporary Equity And Stockholders Equity [Line Items]
Common stock authorized for issuance		12,200,000			12,200,000		12,200,000
Options and restricted stock units outstanding		4,100,000			4,100,000		4,100,000
Options available for future grants		8,100,000			8,100,000		8,100,000
Maximum
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity preferred stock, shares authorized								1,000,000
Series E Convertible Preferred Stock
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity preferred stock, shares authorized								69,565
Temporary equity preferred stock, par value								$ 0.001
Temporary equity preferred stock, shares issued		0			0		0	69,565
Temporary equity preferred stock, shares outstanding		0			0		0	69,565
Series F Preferred Stock
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity preferred stock, shares authorized								18,000
Temporary equity preferred stock, par value								$ 0.001
Private Placement
Temporary Equity And Stockholders Equity [Line Items]
Common stock offered	10,800,000
Exercise price of warrants	$ 0.515
Private Placement | Series E Convertible Preferred Stock
Temporary Equity And Stockholders Equity [Line Items]
Temporary equity numbers of shares sold							69,565
Conversion Of Preferred Stock Into Common Stock		6,956,500			6,956,500		6,956,500
Temporary equity net proceeds from conversion to common stock		$ 4.0			$ 4.0		$ 4.0